The National Weather Service notified lawmakers on Thursday that it plans to furlough up to 5,000 employees for a total of 13 days between July and September if Congress and the agency cannot find $36 million to cover its budget deficit.

But with labor costs of $2 million a day, the Weather Service cannot pay its employees through the end of the fiscal year in September without a solution to a problem of its own making. An internal investigation concluded that for several years, the service reallocated millions of dollars Congress approved for a variety of other projects in order to pay employees.

The investigation prompted the abrupt retirement of the Weather Service’s director, John L. “Jack” Hayes, after the replacement of the agency’s chief financial officer.

The service stopped the practice once the investigation was underway.

Officials at the National Oceanic and Atmospheric Administration (NOAA), which oversees the service, have declined to say publicly why the practice went on and who authorized it. They have asked Congress to cover the gap to get through the fiscal year.

But lawmakers who oversee the Weather Service budget said last week they would not consider the request until they know more about what happened and why. The House appropriations panel that oversees NOAA and the Weather Service has scheduled a hearing on the budget problems for June 21.

“If faced with this difficult situation, [the Weather Service] would work to prioritize resources and staff for mission-critical operations...” agency officials wrote to the National Weather Service Employees Organization about possible furloughs. “Weather operations would likely be affected.”

“Furloughs would also reduce staff or potentially close weather forecast offices and river forecast centers during the time of year when there are significant hurricanes, flash floods, extreme heat and forest fires,” officials wrote.

National Weather Service Employees Organization President Dan Sobien called the furlough notice a negotiating tactic by NOAA to prod action from Congress and the Commerce Department, which began talks last week to find a solution.

He said the effects of furloughs would be devastating, from local forecasting to guidance to air traffic controllers at airports.

“Every aspect of someone’s life is affected by the weather,” Sobien said. “These are operational people. You can’t stop hurricanes or tornadoes because we’re furloughed.”

NOAA spokesman Scott Smullen said that “out of an abundance of caution, we have to prepare for every situation.  We are working with Congress on the reprogramming and we are hopeful we will come to an acceptable resolution to avoid furloughs.  NOAA is committed to doing everything within its authority to avoid furloughs, and our focus will remain on maintaining the critical operations and services we need to successfully perform our mission.”

Sen. Barbara A. Mikulski (D-Md.), chairman of the Senate Appropriations subcommittee on commerce, justice, science and related agencies, said Thursday she opposes any furloughs.

“We cannot allow furloughs because of inept bureaucracy,” Mikulski said in a statement. “I am on the side of the men and women of the Weather Service, and the American people who depend on their forecasts and warnings.” She said she is still working with her Republican colleagues “to get all the facts so we can agree to a new plan to prevent furloughs in the short term.”

 Rep. Paul Broun (R-Ga). chairman of the House subcommittee on investigations and oversight, said his staff has asked NOAA repeatedly to see a copy of the full investigation. NOAA officials said it had been delivered Wednesday.

“Although NOAA and the Department of Commerce refuse to provide details on why and how the Weather Service was robbing Peter to pay Paul, they did find the time to submit a reprogramming request to Congress to address an apparent ‘structural deficit’ that NOAA ignored up until this point,” Broun said in a statement. “Either NOAA turned a blind eye to this deficit, or they were asleep at the wheel.”

The Weather Service staffs 122 forecast offices throughout the country (including Alaska, Guam, Hawaii and Puerto Rico) and key centers such as the National Hurricane Center in Miami, and Storm Prediction Center in Norman, Okla.

These offices issue watches and warnings for violent weather,including severe thunderstorms, tornadoes, flash flooding and hurricanes. The alerts are passed on directly to the public and the media.

Employees say they fear that furloughs coinciding with severe thunderstorm and hurricane seasons could compromise the quality and timeliness of information provided about these hazards.

NOAA officials have said there is no evidence of fraud or personal gain from the misdirected money. But the investigation, prompted by anonymous complaints in 2010 and 2011, concluded that senior Weather Service staff operated “outside the bounds of acceptable financial management.”